I ran a program called avast! antivirus and it picked up a load of viruses which couldn't be deleted. Some referred to the name "services.exe" or similar. Someone please help me, occasionally my pc will just turn off for no reason!

Be sure and put a check in the box by "Auto Clean" before you do the scan. If it finds anything that it cannot clean have it delete it or make a note of the file location so you can delete it yourself.